Not Applicable.
The present invention relates generally to radar, and more particularly, to radar systems having a plurality of antennas.
Phased array radars can have multiple faces each with a predetermined field of view. For example, for a phased array radar having three faces, each face can have a one hundred and twenty degree field of view. While this arrangement may cover three hundred and sixty degrees, there are certain disadvantages associated with such a configuration. The dwell time for a target near the scan boundary of an antenna face, e.g., sixty degrees off boresite, can become unacceptably long since the so-called time on target should be maximized while signal gain is decreased as the scan angle increases. FIG. 1 graphically illustrates the relationship between time on target versus scan angle for an exemplary prior art three-faced radar system. The threshold time on target increases dramatically beyond a certain scan angle.
As known to one of ordinary skill in the art, relatively long dwell times can degrade the overall performance of the radar. For example, since a high speed target may move through multiple range and doppler cells during a long dwell, the computations to process the received signal data are relatively complex and thereby require significant processor overhead. So called target strings must be identified and integrated over the dwell. It will be appreciated that the processing time to perform such computations leave relatively little capacity for the processor to execute other necessary functions. Thus, radar complexity and cost is increased due to the increased number of transmit/receive modules that are required to achieve adequate gain levels at maximum scan angles and the concomitant processor capacity.
It would, therefore, be desirable to provide a radar system that increases signal sensitivity at relatively high scan angles to reduce dwell times.
The present invention provides a multi-faced radar system that cooperatively processes scattered energy from first and second signals, which differ in frequency, transmitted by respective first and second antenna faces. For relatively high scan angles of the first face, first signal return incident upon the first and second antenna faces are combined and second signal return on the first and second antenna faces are combined so as to increase signal sensitivity. The aggregated first and second signal returns are then combined to further increase signal sensitivity. Cooperatively processing first and second signal returns on the first and second antenna faces dramatically decreases the time on target required for relatively high scan angles.
In one embodiment, a radar includes first, second, and third antenna faces spaced from each other so as to cover three hundred and sixty degrees. The first face radiates a first signal having a first frequency and the second face radiates a second signal having a second frequency, which differs from the first frequency. For relatively high scan angles of the first face, e.g., from about 45 degrees to about 60 degrees off boresite, each of the first and second faces illuminate a common area of space so as to provide an overlap region. For a target located in the overlap region, each of the first and second faces receives scattered energy from the first and second signals.
A processor coupled to the first face processes signal energy from the first and second signals individually. The processor is also coupled to the second face for individually processing signal energy from the first and second signals. The first signal energy from the two antenna faces is combined to provide an aggregate first signal return and the second signal energy is combined to provide an aggregate second signal return. This signal aggregation increases the receive cross section to improve the signal sensitivity. In one embodiment, the first signal energy from the first and second faces is combined coherently. More particularly, signal phase information is taken into account. Alternatively, same frequency signals are combined non-coherently using signal amplitudes. The aggregate first and second signals are then combined to further increase signal sensitivity.
By combining signal returns from two faces, for both first and second signals differing in frequency, signal sensitivity is significantly increased and time on target in the overlap region is dramatically reduced.